Light reflectors or reflection devices are utilized in many applications, and are particularly useful for directing light in applications including video recording, motion picture filming, television, etc. Light reflectors may also be utilized in projection applications. Movie projection screens, for example, are often made with a material designed to enhance the reflected brightness and other qualities of the projected image.
In the field of studio lighting, light reflection devices typically reflect or bounce light from a source and towards a subject, or towards portions of the scenery. Reflectors are typically separated from a light source and may be used for controlling shadows, highlights, and/or the effective size of the main light source. For example, a reflector positioned a certain distance away from a light source may accept light from the source and may effectively increase the beam diameter incident on the subject by effectively increasing the separation between the light source and the subject.
Unmodified direct light from light bulbs or direct mid-day sunlight may be described as a specular point source, where the light rays striking the intended subject may predominantly come from a single direction and may cause pronounced shadows, highlights and contrast. This may be known as “hard” light in the industry. Hard light may be sometimes desirable to achieve certain looks and effects in photography, however, in general, a more diffused or “soft” light source may be needed. Soft light refers to light that may tend to “wrap” around objects, casting shadows with soft edges and lowering the contrast and highlights.
Many types of reflection surfaces are used in studio lighting. One type may be a basic white panel typically made from matt or satin finish paper products, such as card stock, foam core board, bristle board etc. Such reflection surfaces are considered diffuse because they exhibit an almost lambertian distribution of reflected light rays. In the projection screen industry, a surface covered with titanium dioxide or magnesium carbonate may have similar reflection characteristics to matt white paper, and may be a reference standard for light reflection, distribution pattern, and/or viewing angles.
Other white reflection surfaces with characteristics similar to that of paper products may be used, including white vinyl, nylon, synthetic fabrics etc. Typically, the white surfaces tend to reflect the visible spectrum wavelengths evenly without discernable shifts in color.
Although light reflected from the previously described types of white reflection surfaces may exhibit a very soft and neutral quality that may be very useful in many studio lighting situations, such materials may suffer from low reflection efficiency. For example, the reflected light may need to be of sufficient brightness to have the desired effect, which may necessitate either that the size of the reflection surface be increased or the reflection surface be moved closer to the intended subject. Situating the reflector surface close enough to the intended subject to have the desired affect may be difficult or not possible, as it may be visible in the shot or otherwise obtrusive. A larger reflecting surface may also suffer from the same problem, and the large physical size may be inconvenient and undesirable on a location. Additionally, larger reflection surfaces may require larger and heavier frames for mounting.
Another drawback associated with previously described reflection surfaces is that the reflected light tends to be extremely homogenous or “flat”. Flat lighting may be lighting that produces very little contrast on the subject, with a minimum of shadows. For example, flat lighting might be similar to light on an overcast day, and could be described as dull and non-dynamic.
Another type of reflecting surface which may be widely used in studio lighting is white synthetic fabric which may be blended with metallic fibers or metallic coatings, which may give a more specular or harder mirror like reflection. This type of reflection surface may offer a mix of white and metallic in different ratios and patterns, such as a “zebra pattern” which may have alternating bands of white and metallic, to fully metallic. Typically, the metallic patterns may be silver or gold colored. Such materials may reflect higher levels of light towards the intended subject due to the specular mirror like characteristics; however, such materials may cast harsh unpleasing highlights or “hotspots” on the intended subject, especially when used with a hard light source such as the direct sun.
A prior art reflection screen as described in U.S. Pat. No. 5,903,392 to Kojima et. al., is shown in FIG. 1. The intended application is for use as a front projection screen, and the screen includes a first sheet 102, which may contain a diffusion coating formed on the top of a clear substrate 104, and a layer of prisms 106 formed beneath clear substrate 104. The triangular prisms 106 are arranged such that their bottom sides lie on the substrate 104 (i.e., the prism apexes 108 face the back of the reflection screen). The axis of alignment of the prisms may extend in a direction perpendicular to the horizontal viewing plane. Disposed beneath layer of prisms 106 is a black absorbing second sheet 110.
The prior art reflection screen 100 may suffer from several drawbacks: The black absorbing second sheet 110, for example, may absorb most of the light that is refracted through the prism layer 106. Thus, the reflection screen exhibits relatively low reflectance. Furthermore, since the prism apexes 108 face the rear surface 110, when the prism apex is approximately 90 degrees, the light incident on the screen from a given incident angle will be reflected in a direction opposite of the incident angle. As shown in FIG. 1, the incident light ray 112 may be incident on the reflection screen 100 at an approximate angle normal to the rear surface 110, while the reflected light ray(s) 114 may exit the reflection screen 100 at angles similar to that of the incident light ray 112. This may create a mirror like reflection or “hotspot” when the screen is viewed from an angle close to the angle of the incident light. This specular hot spotting may make the reflection characteristics unsuitable for use in most applications. The prior art U.S. Pat. No. 5,903,392 teaches that the prism apex angle should be between 90 degrees and 100 degrees to avoid the hotspot drawback. However, the tooling and manufacturing costs of a customized optical sheet that has a diffusion layer on one side and a prism sheet with non standard (i.e., angles other than 90 degrees) prism apex angles, especially on the large format sizes that would be required for most projection screens, may be prohibitively expensive.
Another prior art reflection screen described in U.S. Pat. No. 7,349,154 B2 to Tomoyuka et. al., is shown in FIG. 2. The intended application for this reflection screen 200 is for a front projection screen. The reflection screen 200 includes a top diffusion layer 202, a transparent resin sheet 203, which may be laminated to the bottom surface of the diffusion layer 202, and a prism layer 204 with triangular prisms arranged such that the prism apexes 206 face the back of the reflection screen. The axis of alignment of the prisms may extend in a direction that may be perpendicular to a horizontal viewing plane. Disposed beneath the prism sheet 200 may be a reflection layer 208 or “mirror” layer, which may be made from vacuum depositing or sputtering of aluminum or silver on the prism surface. Due to the arrangement of the prism layer, this reflection screen may also suffer drawbacks similar to those discussed above with respect to the U.S. Pat. No. 5,903,392. For example, for 90-degree prism apexes 206 that face the rear surface 208, light incident on the screen from a given incident angle will be reflected in a direction opposite of the incident angle. This may create a minor like reflection or “hotspot” when the screen is viewed from an angle close to the angle of the incident light. Furthermore, the use of a highly specular minor-like reflecting surface 208 may increase the specular component of light reflected from the reflection screen 200, which may increase undesirable hot-spotting. FIG. 2 depicts incident light rays 210 entering a bottom side of the prism layer 204 and may be reflected as shown by the reflected light rays 212.
There has long been a need for a reflection surface for studio lighting that may have the qualities of soft, diffuse and neutral qualities of a white reflection surface, and which may be also capable of directing the level of light to the intended subject comparable to that of a metallic blended reflection surface, but without the harsh specular components. There also has long been a need for a high reflectance projection screen surface that may exhibit exemplary qualities, yet may be cost effective to manufacture.